A top aide to controversial UK Labour Party leader Jeremy Corbyn has long-standing ties to anti-Israel terrorist groups and would likely be denied a security clearance as a result, a new report has revealed.

Seumas Milne, Labour’s head of strategy and communications, is considered so influential that he has been referred to as “Corbyn’s brain,” and Corbyn, who is considered antisemitic by the vast majority of British Jews, reportedly relies upon him completely.

According to a weekend exposé by The Mail on Sunday, Milne’s links with terrorist groups dedicated to destroying the Jewish state are decades old. A party staff member, speaking anonymously, said, “Seumas has been supporting groups that deny Israel’s right to exist for many years.”

While he was at Oxford University in 1977, Milne traveled to Lebanon and met with PLO terrorists. According to a New Statesman profile, Milne “learned Arabic, heard shots fired in anger, escaped from a blown-up building, and was briefly captured by militiamen.”

Palestinian activist Hussein Agha who has known Milne for years related that the political adviser “went to Lebanon, Syria, and the West Bank — a young boy on a Leftist grand tour. He adopted a Palestinian accent. He used to speak English with Arabs the way they spoke to him.” He added that Milne met with Fatah members while the group still openly called for Israel’s destruction and the ethnic cleansing of its Jewish population. “I met him when he came back,” he told The Mail. “He was not antisemitic, but he was very, very anti-Israel.”

Returning to Oxford, Milne co-founded the Oxford Palestine Campaign, an extremist anti-Israel group. The organization disseminated PLO propaganda and aggressively denounced the 1978 peace treaty between Israel and Egypt, saying, “We must now expect the Palestinians to react in the only way that is left to them: to escalate their armed resistance.”

Agha, who has since been involved in Israeli-Palestinian peace talks, remarked that Milne “thinks I have sold out, become too soft. He is a purist.”

According to the Mail report, Milne eventually developed links with Hamas and took Corbyn to the Middle East to meet with leaders of the Islamist terror group, which still openly states that its goal is Israel’s destruction.

In 2009, Milne stated, “The idea that Israel is a racist state is largely uncontroversial” and charged that Israel was “built on ethnic cleansing.”

In response to the Mail report, a Labour source said: “Seumas Milne does not endorse the Hamas charter. He has criticised it.” The source added, “Seumas has never advocated violence. The right to resist illegal occupation is enshrined in international law.”

On the overlap between Milne’s and Corbyn’s views, one Member of Parliament noted anonymously, “Without a shadow of a doubt, Corbyn trusts Milne more than anyone. I actually think Corbyn is a little bit thick. It’s no exaggeration to say that Milne is Corbyn’s brain.”

Milne has apparently been heavily involved in Labour efforts to deal with accusations of antisemitism against Corbyn and the party. “Again and again, MPs have asked to see Corbyn to talk about antisemitism, and when they got to his room, they found themselves talking to Milne,” the MP said.

In addition to Israel-related issues, The Mail said Milne had defended Russia’s invasions of Afghanistan and Ukraine, and said an IRA attempt in 1984 to assassinate then-prime minister Margaret Thatcher was a “very daring attack.” After 9/11, he wrote that Americans do not understand that they are “hated with such bitterness” because of their “unabashed national egotism and arrogance.” He has also defended the theocratic Iranian regime, which calls for the destruction of Israel, and called protesters against it “Tehran’s gilded youth.”

Sir Richard Dearlove, former head of British intelligence agency MI6, said that as a result of Milne’s history, it would be impossible for him to pass the required security checks to see classified information if Corbyn becomes prime minister.

“Anyone with his sort of background could not be let anywhere near classified information. It would be out of the question,” said Dearlove.

“I am alarmed enough by Corbyn’s past associations, but Milne’s put him beyond the pale. That means Corbyn could not make the judgments and decisions a PM has to make unless he stopped consulting him,” he explained.

“There would be a recommendation made by the head of MI5, who would have to see the PM and say, ‘This man cannot be allowed to see any classified information.’ Either Corbyn would have to cut contact with him — or the head of MI5 would have to threaten to resign, and do it if he still refused. It would blow up into a major constitutional issue, and it would be huge,” Dearlove added.